In a heavy pot, heat oil over medium-high heat. Add in onions and sauté 3-5 minutes, or until translucent.
Add in garlic and sauté for another minute, constantly stirring to make sure it doesn't stick or burn.
Add potatoes, carrots, and water. Bring the water to a boil, then cover and reduce to low. Simmer for 30 minutes, until potatoes are tender (easily pierced with a fork).
Remove the lid and turn off the heat. Add in Worcestershire sauce, soy sauce, ketchup, instant coffee, and curry powder. Stir until dissolved.
Now break up the curry roux into cubes and add into the pot. With the heat still off, add all the roux and stir gently until it has dissolved completely. (Double check that there are no lumps of roux.)
Turn the heat back on to low and return the curry to a gentle simmer with the lid off. Simmer for another 5-10 minutes, stirring often, until the curry reaches your desired thickness.
Serve with rice and enjoy! I also love to serve with my Crispy Tofu Katsu.